It also leaves out the fact that we are not less than forty years from anything resembling practical asteroid mining.

And even then, mining asteroids is extremely unlikely to provide any benefit whatsoever to the global economy, for the very simple reason that the demand for those resources will be far higher among off-world outposts and communities than it will be back on Earth. You wouldn't spend forty thousand dollars shipping a kilogram of platinum to a consumer on Earth when you could spend four thousand dollars shipping it to a consumer on the moon, especially if that sale also turns into an investment that strengthens future sales.

Earth is sitting at the bottom of a steep gravity well, which prevents us from cheaply sending materials into space; it's also surrounded by a thick atmosphere, which prevents things in space from cheaply returning. It is the most literal manifestation of the term "trade barrier," and most of the solar system's resources are on the other side of it. The instant humans begin living in space and using those resources, Earth will ALWAYS be at a competitive disadvantage; and off-world products will begin to replace Earth-made ones almost the instant they become available.